Sonar estimates of seafloor microroughness

Abstract

This paper presents an analysis of the effects of microroughness of the ocean bottom on a sonarsignal. The results best apply to features where the roughness amplitude is less than one-quarter of an acoustic wavelength such as with ripples, beds of rocks, and nodules. The shape of the probability density function {PDF} of the echo envelope is examined in terms of the rms roughness and a new parameter, the correlation area of the bottom. The area is equal to •he product of the x and y correlation distances along the floor. The PDF is shown to be extremely sensitive to small changes in the roughness. Furthermore by determining the rms roughness from standard coherent reflection measurements, the correlation area may be extracted directly from the PDF. Thus both vertical as well as lateral information is obtainable from sonar data. The technique can be used to discriminate between different types of bottoms that may have the same roughness but different correlation areas, for example a floor with ripples versus one with rocks or nodules. The analysis combines {1} a general statistical model employing the Rice PDF IS. O. Rice, in Selected Papers on Noise and Stochastic Processes, edited by N. Wax {Dover, New York, 1954}, pp. 133-294], and {2)a theory originated by Eckart [C. Eckart, J. Acoust. Sue. Am. 25, 566-570 {1953}]. The analysis is applied to sonar data collected from the continental shelf near Cape Hatteras, North Carolina. The results are consistent with the known characteristics of the area.

Coincidence echo statistics

“…Direct measurements of bottom scattering strength, for example, of the type reported by Jackson et al, 11 may be corrupted by angle errors due to coincident echoes. Methods for determining seafloor roughness that depend on measurement of echo strength, for example, Stanton's method, 12 must also be affected by coincidences. Constructing maps of seafloor acoustic backscattering strength, mentioned by de Moustier, 13 is a further process that would be sensitive to coincident echoes.…”

Registration and variability of side scan sonar imagery

“…A representative estimated probability density function for this data set is shown in fig (5 studies of acoustic backscatter [28] in which the Riciandistribution is applied, providing for transformation of the Gaussian distribution to the Rayleigh distribution.…”

“…as well as accounting for the overall ecllO intensity when the return contains both energy from a scattering surface and energy from specular reflection from non-scattering targets [28] . The form of the lUcian distribution is…”

Experimental investigation of scattering from randomly rough elastic cylinders

“…Real part of integrand for infinite cylinder, (a) and (b) represent typical smooth cylinder integrands while (c) and (d) The elastic material properties are the same as Figure As ka increases, variability is shown to increase indicating increased effects due to roughness 49 [3][4][5][6] Backscattering from randomly rough infinite-length elastic cylinders with fractional roughness aja = 0.0131. See Figure 3-5 for details.…”

“…. 50 [3][4][5][6][7] Backscattering from randomly rough infinite-length elastic cylinders with fractional roughness o s /a = 0.02. See Figure 3-5 for details.…”